docs: def sg_log(tensor, opt):
      r"""Log transform a dense tensor
  
      See `tf.log()` in tensorflow.
  
      Args:
        tensor: A `Tensor` ( automatically given by chain )
        opt:
          name: If provided, replace current tensor's name.
  
      Returns:
          A `Tensor`.
      """
      return tf.log(tensor + tf.sg_eps, name=opt.name)